MOLLUSCS. 277 



En^htnil made tlieii- jmi'iile \vaiiii)uiii, or su.c/can/iocA; wliicli was roo-arded as twice as 

 valuable as the white money, or womjwm jiroiicr. Tiiis latter was made from various 

 shells, but mostly from JBusycon. 



Many otlier species of Venus, in its broader sense, are found in the wanner seas of 

 the world, the west coast of America being better supplied than the east. 



Gytherea and its sub-genus Callixta are readily distinguished from Venus by the 

 presence of an anterior lateral tooth in tlie left valve, which fits into a corresponding 

 depression in the other. Like the last genus it is rich in sjiecies, especially in the 

 warmer seas of the world. Our northern ('. convexa has an outline nnicli like that of 

 the qunhog, but its dead white surface does not render it as attractive as its southern 

 relative, CalUsta (/U/antea, which is found on our southern coasts. Cytherea lusoria 

 is a Chinese species, which derives its specific name from the fact that the inhabitants 

 of the celestial empire paint certain figures on the inner surface of the valves, and 

 then employ them in some of their many games of chance. Cytherea scrqHa has a 

 gromul of white or yellow, oxev which is laid a series of zig-zag reddish-brown lines, 

 which require a rather vi\id imagination to be regarded as resembling writing. It 

 comes from the Indian Ocean, as docs the C. erycina. ('. <li(»ie, from the west coast 

 of America, is a remarkable species, from the fact that it is ornamented by a series of 

 long slender spint's, running in a r<iw down the jios- 

 terior side of the shell, from the umlmne.s to the mar- 

 gin. The color is a rosy purple, vaiying considerably 

 in depth. In the more recent systems of classification 

 it is made the type of the genus Dionc. .* 



Meroe embraces a few sjiecies of oval shells, wiiii , ^ ^ ^ ^ 



three cardinal teeth and a long anteiinr tooth. The ^^^ * 

 general shape can be seen from our figure, but there is ^%i _ ^ ': 



nothing of pojudar interest to be saiil conceniing the fig. 297. — /ifcrog. 



species. Dosinia is represented on our shoi-es by a 



species {D. discus), the specific name of which is very apt. The sliell is flat, and 

 nearly circular in outline; the siphons are united, and the foot is l.irge. 



Gemma embraces only a single species, found on our coast, and known under the 

 repetitive name of Gemma gemma. In size it is minute, scarcely more than an eighth 

 of an inch in length, and in color it is a yellowish white, or rosy, tipped posteriorly 

 with an amethystine purple, so that the name is very ajijiropriate. It would ajipear 

 that it was known to the early settlers of this country, and that they sent specimens 

 of it, along with other curiosities, to the old world ; and yet it was unknown to natu- 

 ralists until the year 1834, when the eminent engineer. General Totten, who was a 

 good naturalist withal, published a description of it. It is an active species, founil on 

 sandy shores, where it burrows quicklj-. One of the most interesting facts known in 

 connection with it is that it retains the young inside its valves until the shells are fully 

 formed, sometimes thirty young being found inside of the jiarent shell. 



No species of the genus Tapes occur on our coasts, but the seas of other [paits of 

 the globe contain neai'ly a hundred species. The shells are long, the siphons sei)arate 

 at their extremities, and the long, slender foot spins a byssus. Many of the species 

 are ornamented with zig-zag lines, of darker color, aiul in Europe, especially on the 

 Mediterranean coast, T. geographica is used as an article of food. 



The family Petricolid^ is a small one, and its only member which requires men- 

 tion is the form known as Petricola pholadiformis. This is a thin, long shell, orna- 



